/Engine/Source/Runtime/Engine/Classes/PhysicsEngine/AggregateGeom.h
Calculates a tight box-sphere bounds for the aggregate geometry; this is more expensive than CalcAABB (tight meaning the sphere may be smaller than would be required to encompass the AABB, but all individual components lie within both the box and the sphere)
void CalcBoxSphereBounds ( FBoxSphereBounds & Output, const FTransform & LocalToWorld ) const